Prosthetic limbs

ABSTRACT

An inner liner for a prosthetic limb is provided. The liner comprises a plurality of airflow openings.

The present invention relates generally to prosthetic limb and particularly, although not exclusively, to a robotic prosthetic arm.

A prosthesis is an artificial device that replaces a missing body part, which may be lost through trauma, disease, or congenital conditions. Prosthetics are intended to restore the normal functions of the missing body part.

The present invention seeks to provide improvements in or relating to prosthetic limbs.

An aspect of the present invention provides an inner liner or socket for a prosthetic limb, the liner comprising a plurality of airflow openings.

According to a further aspect of the present invention there is provided a prosthetic arm comprising an outer frame and an inner socket, the outer frame having a plurality of airflow openings and the inner socket having a plurality of airflow openings.

A further aspect provides an inner liner for a prosthetic limb, the liner comprising a plurality of longitudinal flutes.

The limb may be, for example, an arm or a leg.

In some embodiments the present invention relates a transradial prosthesis—an artificial limb that replaces an arm missing below the elbow. In other embodiments the present invention relates to a transhumeral prosthesis—a prosthetic lower and upper arm, including a prosthetic elbow.

In some embodiments the present invention provides or relates to a myoelectric prosthesis, which uses the electrical tension generated every time a muscle contracts, as information.

The liner/socket may have a plurality of longitudinal flutes. The socket may, therefore, have a generally cylindrical and “concertina-like” configuration. This allows, for example, the socket to be expandable and compressible. Vent hols may be formed in the flutes.

The liner/socket may be flexible. The flexibility may be provided by material choice and/or structural form.

In some embodiments the liner/socket is formed from one section, in other a two- or more section liner is provided.

The inner socket may be formed by an additive manufacturing method, such as 3D printing. In some embodiments the liner is formed by selective laser sintering.

The present invention also provides a robotic prosthetic limb, such as an arm, comprising a ventilated outer frame and a ventilated inner liner.

The present invention also provides a prosthetic arm comprising an outer frame and an inner socket, the outer frame having attachment points for receiving a removable cover.

Arms and arm structures formed in accordance with the present invention may further comprise a wrist mechanism and/or a hand.

A further aspect provides a prosthetic hand contains one or more actuators and a main control printed circuit board.

The present invention also provides a prosthetic limb, comprising a ventilated outer frame and a ventilated inner liner.

The limb may further comprise a removable cover portion.

Example Constraints for Aspects and Embodiments

An ‘umbrella’ constraint for the arm is that the user should be happy to wear it for a whole day.

Further examples of broad device-wide constraints are summarized below:

Weight

The unit should be lightweight. Being lighter than a human arm is not necessarily acceptable as many amputees will have become accustomed to not having that mass on the end of their residual limb.

Weight Distribution

It is not enough to simply reduce the overall weight of the device. Consideration should be paid to where the Centre of Mass (CoM) is located. The further from the elbow it is the more tiring the device is to wear.

Battery Life

The device should last a day at least. Everything from the battery selection, to the electronics design, to the mechanical design has been designed to allow a portable battery to provide enough energy for a day's use.

Aesthetics

Any device designed to be worn should take into account aesthetics. Many highly functional, desirable wearable devices have failed commercially because they failed to take this into account.

Risks

The arm is a relatively low risk device; indeed it is a Class I medical device under the Medical Device Directive (MDD) 93/42/EEC. If it fails, the user is not left immobile.

The device is in contact with the skin for extended periods of time. Therefore, there are biocompatibility concerns. Any materials in contact with the skin for extended periods will be independently tested to ISO 10993.

Furthermore, the circuitry of the device is in direct contact with the skin through the metal contacts of the EMG sensors. Protection circuitry is built in to protect the wearer from any faults, and the device is certified to the relevant parts of BS EN 60601. A removable, low-voltage battery power supply is used and cannot be charged in-situ, minimizing the possibility of any dangerous voltages reaching the user.

Different aspects and embodiments of the invention may be used separately or together.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combination other than those explicitly set out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1—exploded view of a prosthetic arm formed according to an embodiment.

FIG. 2—Palmar view of the tendon layout for a three-motor variant of an actuator block.

FIG. 3—Palmar view of the tendon layout for a four-motor variant of an actuator block.

FIG. 4—shows the attachment of the hand to the wrist mechanism.

FIG. 5—Sub-components of the wrist mechanism.

FIG. 6 shows the various features of a socket.

FIG. 7 shows how covering frames compress on the flutes of the socket via a tensioning system.

FIG. 8—Cable entry/exit channels.

FIG. 9—Upper and Lower Clamping Frame Configuration.

FIG. 10—Left and Right Clamping Frame Configuration.

FIGS. 11 to 13 show a socket/liner.

FIGS. 14 and 15 show a socket/liner.

DEFINITIONS

Palmar—the side of something closest to the palm.

Axial Plane—the plane defined by a normal running axial to the object in question. If no object is specified, it should be assumed the term is being used in the broader anatomical way where the axial vector runs from head to foot through the body.

CoM—Centre of Mass

G²—Geometric continuity in the 2nd derivative. Two curves, meet at a point, share a tangent and curvature.

DFMEA—Design Failure Modes Effects Analysis

PCB—Printed Circuit Board

Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein.

Referring first to FIG. 1, there is shown a prosthetic arm 1 designed to fit transradial amputees. It is comprised of three main sub-assemblies; the hand 5; the wrist 10; and the inner socket IS. The inner socket 15 is covered by an outer frame, which in this embodiment is formed from two parts 20, 22. Additionally, optional, swappable covers 24, 26 can be added to style the arm.

The system is actuated by motors concealed within the palm. It is powered by a battery located either just below the elbow or inside the distal end of the arm. The user controls the system by flexing the muscles of their forearm; the system senses these flexes with Electromyographic (EMG) sensors embedded in the socket.

The arm is designed to offer amputees a level of functionality close to more advanced devices such as the BeBionic v3 from Otto Bock and the i-Limb from Touch Bionics, whilst still being affordable.

Mechanical Design Hand

FIG. 2 shows a palmar view of the tendon layout for a three motor variant of the actuator block. The central motor is linked to the thumb (this is omitted from this diagram).

The hand contains the actuators and the main control PCB. Although this places a large proportion of the mass far from the elbow, it means the hand can be fitted to a wide range of transradial amputees. Any hardware placed between the end of the user's residual limb and the wrist limits the range of residual limbs that can be fitted. Amputees with an intact wrist would have a disproportionately long prosthetic arm.

In this embodiment the humanoid hand has four fingers and a thumb. It comes in left and right variants, and a variety of sizes.

A smaller size variant uses a three motor actuator block. In this arrangement, the outer two motors are used to flex the fingers by pulling on a tendon. Motor one flexes the first and second fingers, motor two flexes the thumb, and motor three flexes the third and fourth fingers.

FIG. 3 shows a palmar view of the tendon layout for the four motor variant of the actuator block. The third motor is linked to the thumb, this is omitted from the diagram.

For larger hands, there is space to fit a four motor variant of the actuator block. In this case, the first and second fingers are actuated independently. Motor one flexes the first finger, motor two the second finger, motor three is linked to the thumb, and motor four flexes the third and fourth fingers. The arrangement is shown in FIG. 3.

In this manner, hands with the four motor variant are capable of more dexterous grip patterns such as pinching.

Wrist

Attachment Interfaces

FIG. 4 illustrates the attachment of the hand to the wrist mechanism, and is semi-permanent via three screws radially positioned in hand fastener holes. The screws can be removed along with the hand for maintenance.

The radial torque from the socket to the hand is transmitted via two keys (location keys) so that the radial screws are disassociated and are just providing a pull-off constraint putting the screws in shear which is their strongest property.

Attachment of the wrist to the socket is via eight radial self-tapping fasteners (socket fasteners) that screw into the material of the socket liner. Again the screws are in shear which is utilising their strongest property to resist pull-off loads. In this embodiment the Cheetah material is semi flexible and will heavily resist vibration related unfastening.

Rotating Mechanism

FIG. 5 shows the sub-components of the wrist mechanism. In this embodiment the wrist has been designed to rotate the hand+/−90 deg ° from a neutral position. The neutral position has been defined as the hand in the vertical plane with the thumb upwards. Therefore the hand can be indexed to the palm up or palm down position.

The wrist rotation is naturally locked with a button on the dorsal side of the wrist requiring to be depressed to unlock. Depression of the button releases internal gear teeth allowing indexing of the hand at approximately 7° increments. A spring forces the teeth on the button back into place locking the wrist upon release. There are different (for example two) sizes of wrist diameters, each use the same internal components and mechanism, only the outside diameter and release button length is modified.

Cable Management

The wrist has to allow pass through of both power and EMG signal cables between the hand and the socket components. Because the locking and index mechanism is low profile, an 8-pin connector has been incorporated into the central space, which connects to the hand's main board upon hand fitment. Behind this connector, there is space for a spiral wrap of cables which will expand and contract as the wrist rotates. At the distal end of the socket, the cables will split into two different feeds, one for the EMG circuit on and one for the battery pack. The length of the wrist section is 20 mm and diameters are, for example, 56 mm (large) and 46 mm (small).

Arm

Socket

In this embodiment the socket/liner is printed in the semi flexible Cheetah plastic from Fenner Drives which is a certified medical safe material to ISO 10993, tested by Envigo Laboratory.

Due to the socket's flexibility and design profile, it is both expandable and compressible which allows some growing room and an element of conformality to the user's residual arm shape.

Adjustability of the fit comes from the external panels compressing on the outer surface of the socket via a cable tensioning system.

FIG. 6 shows the various features on a socket 115 formed in accordance with the present invention. The socket 115 includes a proximal socket 116 and a distal socket 117. The interior of the socket is provided with a plurality of longitudinal flutes 118 which have spaced along their length a plurality of vent holes 119.

Ventilation is achieved due to the fluted nature of the socket where small air channels have been incorporated. The fluted channels are printed with holes to allow heat and moisture to escape externally and allow fresh air to permeate through to the skin. In some embodiments covering frames are also aerated via a mesh like structure which helps reduce heat containment.

FIG. 7 shows how covering frames compress on the flutes via a tensioning system and due to the thin walled nature of the flutes, the socket adjusts its diameter to conform to a range of shapes.

In this embodiment the socket is printed in two parts, a fixed distal section which is attached to the wrist via the eight socket fasteners described in FIG. 4 and a removable proximal section that can be washed and cleaned easily. In other embodiments a single-piece socket is formed, for example by an SLS process.

A double section socket can be used to make the 3D printing process of some embodiments more stable by reducing the need to print tall slender flexible objects. The proximal section of the socket is held in place by a locking bead feature which is captivated by the outer frames coupled with a cable tensioning system.

For each patient the optimum EMG sensor position should be attained. The socket has cut-outs shaped so that sensor assembly can be pushed through from the outside to achieve fitment against the skin at the desired location.

Cable management has to pass through from the outside of the arm, through the outer frames and socket into the wrist. The distal end of the socket has channels for the EMG and battery power cables to pass through as shown in FIG. 8.

The flared entry around the elbow has been extended to cover the epicondyle areas to achieve some clamp and prevent the socket from falling off. During a scan rectification phase, these areas can be reworked to give extra clamp. These areas on the clamping frames can also be reworked with heat at the patient fitment phase. Running along the length of the socket are location ridges for the outer frames, this is to stop any radial slip during the tightening process with a cable tensioning system.

Thermoformed Frames

External to the socket are two frames that provide an adjustable clamping force to retain the socket on the arm.

Two example configurations of the arm (which impacts the shape of the frames) are shown. One configuration is to have the battery pack attached externally to the arm and for this the frames is split into an upper and lower configuration 120, 122 (FIG. 9). The second configuration is to have the battery internal to the distal end of the arm and for this the frame is split into a left and right configuration 220, 222 (FIG. 10).

Material Choice

In some embodiments the printed parts are all made from two materials.

The flexible parts such as the ligaments and socket may be made from a TPU designed for 3D printing called “Cheetah” made by a company called Ninja Tek, a subsidiary of Fenner Drives. Cheetah is non-toxic, and certified for long term use in contact with skin.

The rigid parts may be made from PLA, a biodegradable thermoplastic. PLA has been used in medical implant applications 1. The specific PLA used in the OBI is produced by Filamentive. It is stated as being “essentially non-irritating to skin” in the Safety

Data Sheet. No PLA parts are in prolonged contact with the skin so this is considered low risk.

The grip pads may be cast from Vytaflex 30 Urethane rubber.

FIGS. 11 to 13 show a socket/liner 315 formed according to a further embodiment. In this embodiment an exoskeleton is formed by two lattice-like frame sections 320, 322. In this embodiment the section 320 can receive an external battery (not shown) in a holder 321.

FIGS. 14 and 15 show a socket/liner 415 formed according to a further embodiment. In this embodiment an exoskeleton is formed by two lattice-like frame sections 420, 422. This embodiment uses an internal battery configuration with one or more bays for receiving batteries.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. 

1. An inner liner for a prosthetic limb, the liner comprising a plurality of airflow openings.
 2. A liner as claimed in claim 1, in which the liner has a plurality of longitudinal flutes.
 3. A liner as claimed in claim 2, in which vent holes are formed in the longitudinal flutes.
 4. A liner as claimed in claim 1, in which the liner is expandable and compressible.
 5. A liner as claimed in claim 1, in which the liner is flexible.
 6. A liner as claimed in claim 1, in which the liner is formed as a single piece.
 7. A liner as claimed in claim 1, in which the liner is formed from two or more sections.
 8. A liner as claimed in claim 1, in which liner is formed by an additive manufacturing method.
 9. A liner as claimed in claim 1, in which the liner is formed by selective laser sintering.
 10. A prosthetic arm inner liner comprising a liner according to claim
 1. 11. A robotic prosthetic arm comprising a ventilated inner socket.
 12. An arm as claimed in claim 11, further comprising a hand.
 13. A prosthetic limb, comprising a ventilated outer frame and a ventilated inner liner.
 14. A limb as claimed in claim 14, further comprising a removable cover. 